The invention relates to a refrigerator.
In order to cool the interior of a refrigerator, a refrigeration circuit is generally provided in which a refrigerant circulates. Said refrigerant expands in the evaporator mounted in the interior, absorbing heat from the interior. Opening the door causes more or less moist air to enter the cooled interior. During operation, this moisture is first precipitated in the form of frost on the evaporator, then gradually turning into ice. In freezers, the wall temperature is also less than 0° C., so that in the course of time the walls also become coated with a layer of ice. As particularly a thick layer of ice on the evaporator has a negative effect on the transfer of heat from the air in the interior to the coolant in the evaporator, the compressor must be operated for a very long time in order to cool down the interior accordingly. The layer of ice on the evaporator must therefore be removed by defrosting.
Earlier refrigerators had to be manually defrosted by switching them off and opening the doors. The ice layer was allowed to melt and run down into a special container or was removed from the interior after it had become detached from the evaporator or the walls due to the heat introduced. Such defrosting was always a tedious process, as the refrigerated items could not remain in the refrigerator for the defrosting period, which might take several hours, but had to be stored elsewhere. However, it is only by regularly removing the evaporator's coating of ice that low power consumption and therefore efficient refrigeration can be ensured.
Modern refrigerators and freezers generally have automatic defrosting whereby the ice which has formed on the evaporator, reducing its cooling efficiency, is liquefied in order to allow it to run down into a special container. Evaporators of refrigerators of this kind are equipped with a heater which is operated under predefined conditions and raises the temperature of the evaporator to above freezing point. DE 100 53 422 A1 describes automatic defrosting which finds an economically desirable time for the defrosting process on the basis of measuring various parameters.
In order to prevent the refrigerated or frozen items from warming up during the defrosting process, in appliances with automatic defrosting the evaporator is usually accommodated in a compartment sealed off from the refrigerated interior. During the normal cooling phases, an exchange of air between the interior and the evaporator compartment takes place by means of an air circulation system. Said compartment is generally embodied at the back of the refrigerator, sloping down toward one side. The air moisture deposited as ice on the evaporator is thawed automatically or as required and the resulting liquid flows together down the slope to a point in the compartment from where it is fed through the rear wall into a collecting tray located in the machine compartment. There the liquid is evaporated by the waste heat of the compressor. During the defrosting process, the exchange of air between the interior and the evaporator compartment, which feeds the air to be cooled to the evaporator, is interrupted. This means that none of the air heated by the heater is fed to the cooled interior. The defrosting process therefore has no adverse effect on the refrigerated items.
On the outside of the refrigerator, the refrigeration circuit has a condenser which releases the heat absorbed by the refrigerant in the interior to the ambient air. In order to be able to ensure the necessary heat exchange, the condenser must be of a particular size which, particularly in the case of built-in appliances, is at the expense of the size of the refrigerated interior.
If the external dimensions of the refrigerator are retained, enlarging the refrigerated interior involves reducing the size of the condenser. In turn, the condenser now requires a blower capable of removing the heat produced by the condenser. The blower is generally positioned such that it simultaneously also force-ventilates the compressor. Such a design is described in DE 10 2004 058 198 A1. Such blowers are typically operated in parallel with the compressor.
In order to make refrigerators as energy efficient as possible, electrical loads such as compressors or blowers are installed which are designed to provide precisely the required performance and are not overspecified in any way. These electrical loads are therefore of very compact design and require little power.
When the refrigerated interior has reached its preset temperature, operation of the compressor and therefore also of the blower is interrupted and the evaporator absorbs no more heat from the interior of the refrigerator. However, the condenser heats up more strongly when the compressor is not working. This is due to the fact that the pressurized gas is liquefied even after the compressor has shut down, thereby releasing heat. However, this heat is no longer dissipated by the blower. The compressor also continues to give off heat which is likewise no longer eliminated by the blower and additionally heats up the condenser. This can result in the condenser no longer achieving the desired effect and only gaseous refrigerant being present throughout the refrigeration circuit.
When the temperature in the interior has reached a particular level because of the heat introduced due to the insulation or opening of the refrigerator door, the compressor starts up again. For cold generation in the evaporator, liquid refrigerant which can be expanded in the evaporator to the gaseous state is required in the condenser. However, if only gaseous refrigerant is now present in the condenser when the compressor restarts, no cold is initially generated in the evaporator despite the compressor being activated. The cooling capacity of the evaporator is not restored until the blower has cooled the condenser down to a particular temperature and the compressor has been running until correspondingly compressed refrigerant can be liquefied in the condenser.
However, it has been found that, after startup of the compressor, a considerable period of time may elapse until expandable liquid refrigerant is again present in the condenser. This period of time is significantly longer than a normal compressor phase. If a compressor is now designed only for the normal operating time, the compressor will be overloaded by the excessively long operating time, thereby becoming overheated. This overheating may result in activation of the motor protection provided for the compressor, thereby de-energizing the compressor. The compressor will not start up again until its temperature has fallen below a particular level. As this means that no cold refrigerant is fed to the evaporator for a lengthy period and therefore no heat is removed from the interior of the refrigerator, the refrigerated or frozen items stored therein may be damaged.